The present invention relates generally to imaging systems, such as radiographic systems, and more particularly, to digital detectors. Even more particularly, the present invention relates to an apparatus and method for achieving higher pixel pitch in flat panel solid-state detector arrays.
Digital imaging systems are becoming increasingly widespread for producing digital data, which can be reconstructed into useful radiographic images. In one application of a digital imaging system, radiation from a source is directed toward a subject, typically a patient in a medical diagnostic application, and a portion of the radiation passes through the patient and impacts a detector. The surface of the detector converts the radiation to light photons, which are sensed. The detector is divided into a matrix of discrete picture elements or pixels, and encodes output signals based upon the quantity or intensity of the radiation impacting each pixel region. Because the radiation intensity is altered as the radiation passes through the patient, the images reconstructed based upon the output signals provide a projection of the patient""s tissues similar to those available through conventional photographic film techniques.
In available digital detectors, the detector surface is divided into a matrix of picture elements or pixels, with rows and columns of pixels being organized adjacent to one another to form the overall image area. When the detector is exposed to radiation, photons impact a scintillator coextensive with the image area. A series of detector elements are formed at row and column crossing points, each crossing point corresponding to a pixel making up the image matrix. In one type of detector, each element consists of a photodiode and a thin film transistor. The cathode of the diode is connected to the source of the transistor, and the anodes of all diodes are connected to a negative bias voltage. The gates of the transistors in a row are connected together and the row electrode is connected to scanning electronics. The drains of the transistors in each column are connected together and each column electrode is connected to additional readout electronics. Sequential scanning of the rows and columns permits the system to acquire the entire array or matrix of signals for subsequent signal processing and display.
In use, the signals generated at the pixel locations of the detector are sampled and digitized. The digital values are transmitted to processing circuitry where they are filtered, scaled, and further processed to produce the image data set. The data set may then be used to store the resulting image, to display the image, such as on a computer monitor, to transfer the image to conventional photographic film, and so forth. In the medical imaging field, such images are used by attending physicians and radiologists in evaluating the physical conditions of a patient and diagnosing disease and trauma.
One type of digital detector is the large area solid-state detector. Large area solid-state detector arrays provide solutions for digital imaging applications such as medical imaging, digital reproduction and non-destructive testing. As the demands on the resolution of these imaging systems increases, the requirements on the density of the interconnect also increases. The pitch of the system governs the density of the interconnect. In the art, the term xe2x80x9cpixel pitchxe2x80x9d typically refers the spacing between the individual pixels. The drive to have a higher pixel pitch stretches the limits of today""s interconnect technology, as well as severely impacting manufacturability, reliability and yield.
One possible solution for alleviating the interconnect density problem on digital detectors would be to move the electronics on to the panel, either as devices mounted directly to the detector array or by manufacturing the electronics as part of the panel processing. However, panel-processing technology does not yet permit on-panel construction or the necessary electronics, such as preamps and analog to digital converters that are required for panel read out. Even if such high quality devices could be designed, the additional processing costs render the approach cost prohibitive.
Mounting devices directly to the detector array through chip-on-glass construction is also an impractical solution to the interconnect density problem. The panel processing technology may not support a metal top layer, thus limiting the options for bonding the electronics to the glass. Reliability and yield of the panel itself would also be reduced in such approaches. Finally, the speed and low-noise requirements of an imaging system become problematic in such a method. The chip-on-glass method specifically affects the speed and low-noise performances by placing additional constraints on power dissipation.
There is a need, therefore, for a method to provide increased pixel pitch without impacting the density of the interconnect. It is also desirable to increase the pixel pitch without requiring changes in the panel processing technology or a solution through chip-on-glass construction.
The present invention features a digital detector system designed to respond to such needs. One aspect of the technique provides a method for acquiring signals from discrete pixels in a detector. The detector includes a matrix of rows and columns of pixels, whereby each pixel is configured to generate a signal based upon the radiation received from a radiation source. The method includes steps of commanding a multiplexer circuit to select desired rows and columns of pixels, and reading signals from the desired rows and columns.
Another aspect of the technique relates to an imaging system including a source of radiation, a control circuit to regulate the source of radiation, and a detector for receiving radiation from the source of radiation and for generating signals therefrom. The detector has an array of pixels, forming rows and columns coupled to a plurality of scan lines, each scan line being coupled to a plurality of rows of pixels. The detector has a multiplexing circuit for selectively coupling the rows of pixels to respective scan lines for read out of the signals disposed upon the detector.
Yet another aspect of the technique relates to detector comprising an array of pixels. The array of pixels forming rows and columns which are configured to generate signals based upon radiation impacting the detector. The detector also has a plurality of scan lines, wherein each scan line is coupled to a plurality of rows of pixels, and a multiplexing circuit for selectively coupling the rows of pixels to respective scan lines for read out of the signals.